Sound translating device



June 25, 1940.

H. c. PYE 2,205,670

SOUND TRANSLATING DEVICE Fiied July 22, 1938 2 Sheets-Sheet 1 u 1 1. ll40111111111511!!! umnnull/11111111111!!! IN VENTOR.

, Harald]: F e BYMMIMW ATTORNE Y5.

Patented June 25, 1940 UNITED STATES PATENT OFFICE SOUND TRAN SLATINGDEVICE Application July 22,

7 Claims.

1938, Serial No. 220,759

The present invention relates to sound transfree vibration, togetherwith means associated lating devices and more particularly toimprovements in diaphragm assemblies for telephone receivers.

In the conventional telephone receiver, a diaphragm is provided whichforms a part of the magnetic circuit of the associated field structureand vibrates in response to variations in the flux traversing the fieldstructure and occasioned by signal currents flowing through the voicecoils wound on the pole pieces of the field structure. Usually thediaphragm is mounted for substantially free vibration by clamping itsouter edge between two of the field structure housing members. As thusmounted, the diaphragm has a frequency-response characteristic over theoperating range which peaks at frequencies in the vicinity of thenatural frequency of vibration of the diaphragm and falls off at thehigher frequencies of the operating range due to the mechanical inertiaof the diaphragm. For the purpose of flattening the resonance peak inthe response characteristic of the diaphragm, various forms of frictiondamping means and damping chambers have been used. In some cases it hasalso been the practice to use resonating chambers for the purpose ofenhancing the response of the diaphragm at the high frequency end of theoperating range.

It is an object of the present invention to provide an improved assemblyfor the moving system of a sound translating device which is so arrangedthat an improved and relatively flat response characteristic is obtainedthroughout the operating frequency range.

It is another and rmare specific object of the invention to provide in adevice of the character described an improved and exceedingly simplearrangement of the parts whereby a damping effect is exerted on one sideof the diaphragm or vibratory member and a resonating chamber forenhancing the response of the diaphragm at the high frequency end of theoperating frequency range is provided on the other side of thediaphragm.

It is a further object of the invention to provide a simple, rugged,compact and economical assembly arrangement for the vibratory member of"a sound translating device.

attained by providing, in a sound translating device, a moving systemwhich comprises a ,vi-

bratory member having a predetermined response characteristic over :anoperating fre- 55 quency range when arranged for substantially Ingeneral, the objectsas set forth above arewith one side of the vibratorymember for altering the response of the moving system over one band offrequencies within the operating range-and means associated with theother side of the vibratory member for altering the response of themoving system over a diflerent band of frequencies within the operatingfrequency range. More particularly, the diaphragm or vibratory member ofthe device is mounted within 10 the housing of the device, together withan inner plate which is displaced from the diaphragm to provide adamping chamber adjacent the inner side of the diaphragm. A structurecomprising a second plate mounted upon the inner plate in 1 spaced-apartrelation is provided for defining a passage communicating with thechamber, the dimensions of the passage being such that the response ofthe diaphragm is substantially reduced at frequencies approaching thenatural frequency of vibration of the diaphragm. The housing for thedevice is also provided with a cover portion which is displaced from thediaphragm to define a second chamber adjacent the outer side of thediaphragm. The cover portion of the housing is provided with a passageextending therethrough and communicating with the second chamber, thedimensions of this passage being so proportioned that the response ofthe diaphragm is substantially increased at the upper end of theoperating frequency range. Further features of the invention pertain tothe particular arrangement of the assembly whereby the two chambersdescribed above are provided.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. The invention, bothas to its organization and method of operation, together with furtherobjects and advantages thereof, will best be understood by reference tothe specification taken in connection with the accompanying drawings inwhich Figure 1 is a side sectional view illustrating a sound translatingdevice having incorporated therein the features of the invention asoutlined above, Fig. 2 is an elevational view of the device shown inFig. 1 with the diaphragm assembly removed therefrom, Fig. 3 is anexploded view illustrating .the method of assembling the device shown inFig. 1, Figs. 4 and 5 are detail views of certain of the elements shownin Figs. 1 and 3, Figs. 6 and 7 are detail views of modifications ofcertain of the elements embodied in the device, and Figs, 8 and 9 aregraphs illustrating the effect of providing the two' chambers on the twosides of the diaphragm in the manner referred to above.

Referring now more particularly to Fig. 1 of the drawings, there isillustrated a sound translating device in the form of a telephonereceiver of the cell type mounted within the cup-shaped portion 1 of ahand set handle. The cell is supported between the rim of the cupshapedopening and the inner wall of a cupshaped ear piece 8 which is adaptedto be screws; on the threaded portion of the portion 1 in the mannerillustrated. The ear piece is provided with eight sound transmissionholes 9 in the bottom wall thereof and also with a cutaway portion whichforms a chamber adjacent the cover member of the cell. The receiver cellcomprises a cup-shaped housing l constructed of non-magnetic conductivematerial, such, for example, as an aluminum alloy, and having mountedthereon the magnetic field structurematerial, such, for example, assilicon steel,

having a high A. C. permeability. The magnetic field structure of thedevice comprises a pair of pole pieces l4 and I5, upon which the voicecoils l6 and ll of the receiver are wound, and a permanent magnet 18 ofthe bar type which, in conjunction with the diaphragm l3 and the polepieces l4 and I5, forms a substantially closed magnetic c'rcuitinterrupted only by the narrow air gaps extending between the pole facesof the pi Cos l4 and I5 and the diaphragm i3. More p;:.rticularly, thepole pieces 04 and I5 are re specai' ly provided with offset extensions'43. and '55, which extend through snugly engaging spaced pfart openingsl9 and 20 cut in the bottom of the cup-shaped housing member Ill and arearranged to receive a magnet member I8 therebetween. For the purpose ofretaining the magnet bar l8 within the pole piece extensions I45 and15s, the upper corners, and more particularly the edges, of the magnetbar are beveled as indicated at '89. and lab, and the upstanding cornerportions of the pole piece extensions He and 15;. are bent over toengage the beveled edges the magnet bar in the manner best illustratedin Fig. 5. Preferably, the length of the bar is just slightly greaterthan the spacing between the pole piece extensions I411 and I5; so thatthe oppositely disposed bases of the pole piece etr'iensions Ma and I5&firmly engage the adjacent faces of the magnet bar to provide a lowreluctance connection between the pole pieces and the magnet bar. Itwill be noted that the mounting arrangement just described serves torestrain the magnet bar 18 against movement in any direction and, thus,this bar is rigidly held in place when the assembly of the device iscompleted.

The magnet bar I8 is preferably formed of an alloy consisting of nickel,aluminum and iron, such, for example, as the alloy known as Alnic; whilethe pole pieces I4 and 15 are formed of an alloy comprisingapproximately 45 per cent nickel and 55 per cent iron, such, forexample, as the alloy known as Allegheny electric meta The magnetwinding I6 is wound upon the pole piece l4 between winding heads 2| and22 constructed of insulating material and is insulated aaoacvo from thepole piece M by a layer of insulating material 23 which may, forexample, comprise varnished cambric or Empire cloth. The ends of thewindings l6 are brought out through slots provided in the inner sidewalls of the winding heads 2| and 22 to anchoring studs 2'3, and 22aformed integrally with the winding heads 2| and 22, respectively, andprojecting therefrom. In a similar manner, the winding I1 is wound uponthe pole piece l5 between winding heads 24 and 25 and is insulated fromthe pole piece l5 by a layer of insulating material 26. The ends of thelast-mentioned winding are brought out through slots provided in theinner side walls of the winding heads 24 and 25 to anchor studs 24a and258. formed integrally withand projecting from the winding heads 24 and25, respectively. In accordance with conventional practice, the twowindings l6 and H are connected in series by soldering together the endsof the windings terminating at the anchor studs 22a and 24a. Theremaining two winding terminals are brought out and connected to theconnecting terminals of the device which, in the arrangementillustrated, comprises the conductive housing l0 and a U-shaped contactmember 21 having its legs straddling the magnet member l8 and secured tothe housing [0. More specifically, the ends of the legs of the contactmember 21 are bent over and provided with holes, 28a and 28]: thereinwhich register with holes 299. and 29b formed in the housing In. Thecontact member 21 is mounted upon the housing In by rivets 30a and 30bextending through the openings 28a, 29a, and 28b, 29b, respectively, andis insulated from the housing It] by insulating washers 3'11, 31 32a and32b in the manner illustrated.

As indicated above, the housing l0 through which the pole pieceextensions 4a, and I5; extend is closely coupled with the magneticcircuit of the field structure and effectively constitutes ashort-circuited conductor encircling each of the two pole pieces l4 andI5. The close inductive coupling between the housing and the magneticcircuit of the field structure results from the fact that the side wallsof the openings l9 and 20 closely embrace the pole piece extensions I48and I5. to provide support for the field structure and to prevent theentrance of dirt and moisture within the housing l0. With thisarrangement, alternating or undulating flux traversing the pole piecesl4 and I5 and the magnet bar l8 necessarily caused induced voltages tobe set up in the conductive housing In, so that a portion of thealternating current energy producing the alternating flux is dissipatedas hysteresis and eddy current losses in the housing. In order toprevent alternating flux developed during operation of the device fromlinking with the housing In, there is provided within the housing anauxiliary flux path extending between the two pole pieces. Thisauxiliary flux path comprises projections I41, and l5s formed integrallywith the pole pieces l4 and I5, respectively, and extending toward eachother. The adjacent ends of the projections Mn and lit are separated byan air gap 33 which is so proportioned that the magnet bar I8 is noteffectively short-circuited and a substantial amount of the steady stateflux produced by the magnet I8 is caused to traverse the diaphragm l3.Preferably, this air gap is of the order of .0625 inch. These polepieces I4 and I5 are stamped from flat stock and during the stampingoperation there are cut in the projecting portions Nb and I51 thereof aplurality of openings 34 and 35, which are utilized in securing the polepieces to the housing I0. More particularly, the pole pieces I4 and I5are mounted upon the housing III by means of rivets or bolts 35 and 31extending through the openings 34 and 35, respectively, and throughopenings 38 and 39 formed in the bottom portion of the housing I andspaced to register with the openings 34 and 35.

The diaphragm assembly comprises, in addition to the diaphragm I3, aninner plate 40, a cover member 4|, an annular supporting and spacingring 42, and an assembly ring 43. In accordance with one feature of thepresent invention, the innerplate 40, in conjunction with the diaphragmI3 and the annular ring I2, defines a damping chamber adjacent the innersurface of the diaphragm I3, while the cover member H, in conjunctionwith the diaphragm I3 and the ear piece 8, defines a resonating chamberadjacent the outer surface of the diaphragm. The dimensions of thedamping chamber and of the restricted passages communicating therewithare so proportioned that the peak in the response characteristic of thedevice caused by the natural period of vibration of the diaphragm I3 issubstantially reduced to flatten the over-all frequency responsecharacteristic of the device. More particularly, the inner plate 40,which is constructed of non-magnetic material, such, for example, asaluminum, is provided with six openings 44 and has mounted thereon inspacedapart relation a fiat annular ring 45 which defines a realtivelylong, narrow, restricted and annular passage 45 communicating betweenthe interior of the housing I0 and the chamber formed between the plate40 and the diaphragm I3. By suitably proportioning the size of the holes44, and the length and width of the restricted passage 45, there isachieved the desired damping effect over the band of frequencies withinwhich the natural period of vibration of the diaphragm I3 is mosteffective to cause distortion of the over-all response characteristic.Also, the layer of air in this chamber serves artificially to enhancethe stiffness of the diaphragm I3, thereby to improve the fidelity ofreproduction of the device. Although given by way of example only, thefollowing specifications for the parts defining the dimensions of thedamping chamber and the passages communicating therewith have been foundto be highly satisfactory in practice:

Inches Diameter of chamber 1.683 Depth of chamber 0.030 Diameter ofholes 44 0.076 Depth of passage 45 0.0030 to 0.0040 Width of ring 450.319 Outer diameter of ring 45 1.444

As best shown in Fig. 4, the annular ring or plate 45 is separated fromthe inner plate 40 by means of thin washers 41 and is mounted upon theplate 40 by means of rivets 48 extending through the washers andregistering with openings 49 and 50 respectively provided in the plate40 and the ring 45. As best shown in Fig. 3, the openings 49 and 50through which the mounting rivets 48 extend are staggered so that theassembly comprising the plate 40 and the ring 45 is prevented frombuckling. The plate 40 has formed therein a pair of slots 0a. and 40bthrough which the pole face ends of the pole pieces I4 and I extend. Across-slot 40c connecting the two slots 40. and 40b is also provided forpreventing the circulation of eddy currents in the plate 40. Thedimensions of the slots 40B. and 40s are substantially greater than thecross-sectional dimensions of the pole face ends of the pole pieces I4and I5 so that relatively large air gaps are provided between theadjacent surfaces of the pole pieces and the plate 40. By virtue of thisarrangement, the coupling between the magnetic circuit of the magneticfield structure and the plate 40 is extremely loose and theproduction ofeddy currents in the plate is substantially prevented.

An alternative arrangement for providing the restricted passagecommunicating with the damping chamber is illustrated in Fig. 6. In thisarrangement a plurality of annular plates or rings 45a, 45b and 45c areprovided which are mounted in spaced-apart and stacked relation upon theinner plate 40 to define a plurality of narrow annular passagesconnected by staggered openings 54 cut in the enumerated rings. Theannular passages are closed at the sides by annular supporting rings 55and 55 which serve to support the plates 59., 45b and 45c inspaced-apart relation. Rivets indicated at 51 are utilized to secure thestacked assembly to the inner plate 40. The holes 44 provided in theplate 40 register with the restricted passages defined by the stackedplates 55., 45b and 45.: and the spacing between the plates is soproportioned that the response of the diaphragm I3 is substantially reduced at frequencies approaching the natural frequency of vibration ofthe diaphragm.

Another arrangement for providing the restricted passage communicatingwith the damping chamber is illustrated in Fig. 7. In this arrangement aplurality of annular plates 58 and 585 are provided which are mounted inspacedapart stacked relation upon the inner plate 40 to define arelatively long' narrow sinuous passage. More particularly, the innerring 55 is mounted upon the plate 40 by means comprising a spacing ring59 and rivets 50, and the outer ring 58a is mounted upon the plate 40 bymeans comprising a spacing ring 5| and rivets 52. The openings 44provided in the plate 40 register with the sinuous passage thus formed,and the spacing between the rings is so proportioned that the responseof the diaphragm I3 is substantially reduced at frequencies in thevicinity of the natural frequency of vibration of the diaphragm.

It will be observed that, in each of the three arrangements respectivelyillustrated in Figs. 1, 6 and '7 for defining the passage communicatingwith the damping chamber, the passages are formed parallel with thediaphragm I3. By virtue of this arrangement, only a small amount ofspace is required to form a passage of any desired length. Moreover, thedepth of the passage is easily controlled by using spacing washers orrings of the appropriate thickness to provide the correct depth.

The cover member M, which, in conjunction with the diaphragm I3, definesa resonating .chamber adjacent the outer surface of the diaphragm, isprovided with a centrally disposed opening 5I through which sound wavesare transmitted from the resonating chamber to the exterior of thedevice. The cover member H is also provided with a projecting annularportion 52 having a smooth upper surface which is adapted to cooperatewith the oppositely disposed lower surface of the annular ring portionI2 of the housing I 0 to clamp the peripheral edge of the diaphragm I3therebetween. The clamping surfaces of the two annular portions I2 and52 are so formed that the peripheral edge of the diaphragm i3 is clampedtherebetween with uniform pressure at all points around the outercircumference of the diaphragm. The effect of the resonating chamberupon the response of the diaphragm I3 is determined to a certain extentby the narrow chamber formed between the inner bottom wall of the earpiece 8 and the outer surface of the cover member 4i. Actually thissecond chamber may be considered as a part of the resonating chamber.Preferably, the dimensions of the resonating chamber and of the passage5| are so proportioned that the natural period of vibration of thechamber occurs at approximately 2700 cycles per second, whereby theresponse of the moving system is materially enhanced at frequencieslying within the band extending from 2400 to 2800 cycles per second. Toachieve this greater response in the frequency band indicated, it hasbeen found that the following dimensions for the resonating chamber andthe passages 5| and 9 are satisfactory:

Inches Outer diameter of chamber adjacent diaphragm 1.688 Maximum depthof chamber 0.033 Diameter of passage 5! 0.250 Depth of passage 5| 0.051Diameter of passage 9 a- 0.1015 Diameter of chamber adjacent ear piece0.750 Depth of chamber adjacent ear piece 0.062

In constructing the device described above, the terminal member 21 isfirst mounted upon the housing ID in the manner explained previously,and the extensions Ma and l5a of the pole pieces 14 and I5 are insertedthrough the openings l9 and 20, respectively. The last-mentionedoperation is performed with the windings l6 and I! fully assembled onthe pole pieces l4 and I5. After the pole piece extensions '43. and '53,have been inserted through the openings l9 and 20, the magnet member I8,which is at this time demagnetized, is forced between the adjacentopposite side surfaces of the pole piece extensions, and the extensionsare pressed toward each other to bring the inner surfaces thereof intofirm engagement with the pole faces of the magnet member l8.Simultaneously, the projections Nb and l5b of the pole pieces 14 and i5are pressed against the bottom wall of the housing l0. While theabove-mentioned forces are acting upon the pole pieces l4 and 15, therivets 36 and 31 are inserted through the openings provided in thehousing l and the pole pieces, and the ends thereof are flattened in theusual manner, thereby rigidly to mount the field structure upon thehousing In. Also, while the above-mentioned forces are being exertedupon the pole pieces l4 and I5, the upstanding corner portion of thepole piece extensions [49, and I55 are bent over against the beveledcorners I89. and I8b of the magnet member l8. After the field structureassembly is completed in the manner just described, the diaphragmassembly is mounted upon the rim of the cup-shaped housing ii). To thisend, the inner plate 40 is forced within the snugly engaging side wallsof the annular ring H! to abut against the ledge formed by the lowersurface of the housing flange II. This operation is performed with theflat annular ring 45 mounted upon the plate 40, and during theperformance thereof the pole face ends of the pole pieces l4 and I passthrough the slots 40a and it provided in the plate 40. The inner plate40 is rigaaoaevo idly held within the annular portion ll! of the housing10 by staking the inner surface of the ring portion 12 at spaced pointsaround the circumference thereof in a well-known manner. Also, a sealedjoint is provided between the plate 40 and the pole face ends of thepole pieces l4 and I5 by pouring an insulating compound, such, forexample, as Bakelite cement, through the spaces between the side wallsof the slots 08. and 40s and the side surfaces of the pole pieces l4 andI5, thereby to insure that the damping chamber shall only be connectedwith the interior of the housing ill by way of the restricted passage 46described above. The next step in the construction of the device is toclamp the diaphragm l3 between the clamping surfaces of the two ringportions l2 and 52 projecting respectively from the housing l0 and thecover member 4|. While the diaphragm is clamped in position, theassembly ring 43 with the annular ring 42 inserted or telescoped thereinis telescoped over the cover member 4| until the flanged portion 433,thereof engages the tapered surface of the cover member 4|, followingwhich the rim of the retaining ring 43 is bent over as indicated at 43bto engage the underside of the flanged portion ll of the housing I 0.The final step in the construction of the device is that of magnetizingthe magnet member l8 by positioning this member in a strong directmagnetic field. After the device is fully constructed it may be mountedwithin the opening of the cup-shaped member I in an obvious manner.

In the operation of the device constructed and arranged in the mannerset forth above, an attractive force is normally exerted upon thediaphragm l3 by virtue of the flux produced in the magnetic fieldstructure by the magnet member l8. Due to the length of the air gap 33,t! magnet member I8 is not short-circuited and a substantial portion ofthe flux traverses the diaphragm l3. When incoming signal currentstraverse the voice coil windings I6 and H, the

steady state flux is increased and decreased in the usual manner inaccordance with the undulations of the signa currents. The change in theflux traversing the pole pieces l4 and I5 causes induced voltages to bedeveloped in the closely coupled conductive housing ill. The resultingcirculatory currents cause back electromotive forces to be developedwhich oppose the flux changes in the usual manner. Thus, the reluctanceof the portion of the magnetic circuit comprising the permanent magnetl8 and the pole piece extensions 4a and '53. is effectively increased sothat the greater portion of the alternating components of the fluxtraverse the auxiliary path described above and comprising the polepiece projections Mb and I5b and do not link with the housing l0. As aresult, only a small portion of the signal current energy is dissipatedas hysteresis and eddy current losses in the housing Ill. The variationsin the flux traversing the diaphragm l3 cause this diaphragm to vibratein the usual manner so that sound waves are transmitted by way of theopening 5| to the exterior of the ear piece 8. The provision of theinner damping chamber defined by the plate 40 prevents an excessiveresponse of the diaphragm l3 at frequencies approaching the naturalfrequency of vibration of the diaphragm. Also, the provision of theresonating chamber defined by the ear piece 8 enhances the response ofthe moving system at frequencies in the upper portion of the operatingrange. Thus, a substantially fiat response characteristic typifying goodfidelity of reproduction is obtained.

The effect of providing the two chambers on opposite sides of thediaphragm l3 and of varying the dimensions of the passages respectivelyextending thereto is well illustrated by the graphs shown in Figs. 8 and9, wherein the response of a typical receiver, measured in decibelsabove one bar pressure is plotted as a function of frequency. In Fig. 8the curve A represents the response characteristic of a receiver cellprovided with a damping chamber adjacent the inner side thereof and aresonating chamber of the form just described adjacent the outer sidethereof; a passage 5| having a diameter of .346 inch being provided inthe cover member 4|. It will be noted from an inspection of this curvethat the response of the diaphragm drops off appreciably at frequenciesabove 2200 cycles per second. This decreased response at the highfrequency end of the band is due to the stiffness or mechanical inertiaof the diaphragm and becomes even more pronounced when the passage 5| ismade of larger diameter further to decrease the effect of the chamberresonance on the vibration of the diaphragm. The curve B is the responsecharacteristic of the same receiver provided with a passage 5| havingadiameter of .255 inch rather than a diameter of .346 inch. In the lattercase the effect of resonance on the diaphragm is enhanced, so that theresponse of the diaphragm over the band of frequencies extending from2200 to 2800 cycles is substantially increased. This increase inresponse at the high frequency end of the band is accompanied by aslight decrease in response at frequencies within the mid portion of theoperating frequency range, but the loss of response at the mid-rangefrequencies is of no practical importance. The increased pressure outputat the high frequency end of the frequency range, however, results in amarked improvement in the fidelity of reproduction of the receiver.

Referring now to Fig. 9, the curves there reproduced illustrate theeffect of providing the damping chamber adjacent the inner side of thediaphragm and of varying the dimensions of the restricted passagecommunicating with this chamber. More particularly, the curve C depictsthe response characteristic of the diaphragm when provided with aresonating chamber adjacent the front or outer side of the diaphragm andno damping chamber is provided adjacent the inner side of the diaphragm.Due to the resonant response of the diaphragm at frequencies approachingthe natural frequency of vibration of the diaphragm this response curvepeaks sharply at approximately 1175 cycles per second. This sharp peakis indicative of distortion in the reproduced output of the receiver.The curves D, E and F depict the response characteristic of the samereceiver when provided with a damping chamber adjacent the inner sidethereof and constructed in the manner shown in Fig. 1. The differencesin the three last-mentioned curves represent the change in the responseof the diaphragm effected when the dimensions of the passagecommunicating with the damping chamber and defined by the plates 40 and45 are changed. Thus, the curve D depicts the response characteristic ofthe receiver when a passage 46 having a depth of .004 inch is used; thecurve E represents the response of the receiver when a passage 46 havinga depth of .003 inch is used; and the curve F illustrates the responseof the receiver when a passage 46 having a preferred depth of .0035 inchis used. It will be observed that the provision of the damping chamberhaving a passage 46 communicating therewith materially reduces theresponse of the diaphragm at frequencies in the low frequency end of therange and approaching the natural frequency of vibration of thediaphragm. Moreover, by properly proportioning the dimensions of thepassage 46 the response characteristic is rendered substantially fiatover the major portion of the operating frequency range. This flatteningof the response characteristic represents a marked improvement inthe-fidelity of reproduction of the device.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. In a sound translating device, a moving system comprising a vibratorydiaphragm and having a predetermined response characteristic over anoperating frequency range when arranged for substantially freevibration, means defining a first chamber adjacent the inner side ofsaid diaphragm having a passage communicating therewith, the dimensionsof said passage being so proportioned that said first chamber actssubstantially entirely as a damping chamber effective substantially todecrease the response of said moving system at frequencies within a bandof frequencies extending toward the low frequency end of said range, andmeans defining a second chamber adjacent the outer side of said memberhaving a passage communicating therewith, the dimensions of saidlast-mentioned passage being so proportioned that said second chamberacts substantially entirely as a resonating chamber effectivesubstantially to increase the response of said moving system atfrequencies within a band of frequencies extending toward the highfrequency end of said range.

2. In.a sound translating device, a housing, a diaphragm mounted withinsaid housing, said diaphragm having a predetermined responsecharacteristic over an operating frequency range when mounted withinsaid housing for substantially free vibration, said diaphragm having anatural frequency of vibration such that said response characteristicpeaks at frequencies within the low frequency end of said range, meansdefining a first chamber adjacent the inner side of said diaphragmhaving a passage communicating therewith, the dimensions of said passagebeing so proportioned that said first chamber acts substantiallyentirely as a damping chamber effective to remove said peak from theresponse characteristic of said diaphragm and substantially to decreasethe response of said diaphragm at frequencies within a band offrequencies extending from a frequency of the order of 1500 cycles persecond toward the low frequency end of said range, means defining asecond chamber adjacent the outer side of said diaphragm having apassage communicating therewith, the. dimensions of said last-mentionedpassage being so proportioned that said second chamber actssubstantially entirely as a resonating chamber effective substantiallyto increase the response of said diaphragm at frequencies within a bandof frequencies extending from a frequency of the order of 2000 cyclesper second toward the high frequency end of said range.

3. In a sound translating device, a housing, a diaphragm mounted withinsaid housing, said diaphragm having a predetermined responsecharacteristic over an operating frequency range when mounted withinsaid housing for substantially free vibration, said diaphragm having anatural frequency of vibration such that said response characteristicpeaks at frequencies in the low frequency end of said range, an innerplate mounted within said housing and displaced from said diaphragm todefine a first chamber adjacent the inner side of said diaphragm, meanscomprising a second plate mounted upon said inner plate in spaced apartrelation for defining a passage communicating with said first chamber,the spacing between said plates being so proportioned that said firstchamber acts substantially entirely as a damping chamber effective toremove said peak from the response characteristic of said diaphragm andsubstantially to decrease the response of said diaphragm at frequencieswithin a band of frequencies extending from a frequency of the order of1500 cycles per second toward the low frequency end of said range, meansdefining a second chamber adjacent the outer side of said diaphragmhaving a passage communicating therewith, the dimensions of saidlast-mentioned passage being so proportioned that said second chamberacts substantially as a resonating chamber effective substantially toincrease the response of said diaphragm at frequencies within a band offrequencies extending from a frequency of the order of 2000 cycles persecond toward the high frequency end of said range.

4. In a sound translating device, a cup-shaped housing member having anoutwardly extending ledge displaced inwardly from its rim along theinner wall thereof, a diaphragm having its outer edge clamped to the rimof said housing member, said diaphragm having a predetermined responsecharacteristic over an operating frequency range when mounted upon saidhousing member for substantially free vibration, an inner plate mountedupon said ledge within said housing and displaced from said diaphragm todefine a chamber adjacent the inner side of said diaphragm, and meanscomprising a second plate mounted upon said inner plate in spaced apartrelation for defining a passage communicating with said chamber, thespacing. between said plates being so proportioned that the response ofsaid diaphragm is substantially altered in one sense over a band offrequencies within said range.

5. In a sound translating device, a cup-shaped housing member having anoutwardly extending ledge displaced inwardly from its rim along theinner wall thereof, a diaphragm having its outer edge clamped to the rimof said housing member, said diaphragm having a predetermined responsecharacteristic over an operating frequency range when mounted upon saidhousing member for substantially free vibration, an inner plate mountedupon said ledge within said housing and aaoaevo displaced from diaphragmt0 define a chamber adjacent the inner side of said diapm'agm, saidplate having a plurality of spaced apart openings therein, and meanscon'orising a flat annular plate overlying said :pening and mounted uponsaid inner plate in spaced apart relation for defining a passagecommunicating with said chamber, the spacing between said plates beingso proportioned that the response of said diaphragm is substantiallyaltered in one sense over a band of frequencies Within said range.

6. In a sound translating device, a housing, a diaphragm mounted withinsaid housing, said diaphragm having a predetermined responsecharacteristic over an operating frequency range when mounted withinsaid housing for substantially free vibration, an inner plate mountedwithin said housing and displaced from said diaphragm to define achamber adjacent the inner side of said diaphragm, said inner platebeing constructed of non-magnetic condui iive material and beingprovided with a pair of spaced apart openings connected by a cross-slot,a field structure 'at least partially enclosed by said housing andincluding pole pieces projecting through said openings out of contactwith the walls thereof, insulating material closing said cross-slot andthe space between said pole pieces and the walls of said openings, andmeans comprising a second plate mounted upon said inner plate in spacedapart relation for defining a passage communicating with said chamber,the spacing between said plates being so proportioned that the responseof said diaphragm is substantially altered in one sense over a band offrequenries within said range.

7. In a sound translating device, a cap-shaped housing member having anoutwardly xtending flanged portion carrying an annular rim a diaphragmadapted to have its outer edge clamped to said rim, said diaphragmhaving a predetermined response characteristic over an operatingfrequency range when clamped to said rim for substantially freevibration, a cover member provided with an annular surface for clampingthe edge of said diaphragm to said rim and having a portion displacedfrom said diaphragm to define a chamber adjacent the outer side of saiddiaphragm, said cover member being provided with a passage communicatingwith said chamber, the dimensions of said passage being so proportionedthat the response of said diaphragm is substantially altered over a bandof frequencies within said range, means comprising an assembly ringhaving a flange engaging the outer side of said cover member and adaptedto have its side walls bent over to engage the flanged portion of saidhousing member for clamping said cover member and said diaphragm to saidrim, and a supporting ring telescoped within said assembly ring andsurrounding said annular rim and the outer edge of said cover member.

HAROLD C. PYE.

